Statement. (Reasons are in boldfaced words)
1. H is the midpoint of AD. By given.
2. AD bisects GC. By given.
3. HA = HD. By definition of midpoint.
4. GH = CH. By definition of the bisector.
5. Angles AHG and DHC are congruent. By vertical angles theorem.
6. AG = DC. They are the height of the figure.
7. Triangles GHA and CHD are congruent. By Side-Angle-Side postulate of congruence.